Evidence of speciation in macroevolution Speciation is a process that in some cases might happen relatively quickly, but usually it takes a very long period of time. Studying fossils gives us an idea of how speciation occurred in the past. Trilobites were a group of aquatic arthropods that were abundant and diverse during the Paleozoic era. They first appeared around 525 million years ago, but by 200 million years ago, they disappeared. No fossils of trilobites have been found that lived more recently than 200 million years ago, and there are no living trilobites today. Thus, we can say that the animals known as trilobites are hiding speciated extinct Imagine that you are working with a paleontologist-someone who studies ancient life-to study the evolution of two particular groups of trilobite fossils. One group of these fossils was collected from dig sites in North America and another group from sites in South America. Both groups of fossils, from each of these continents, bear structural similarities with one another, so they are considered to be either the same species or closely related species. The age of each fossil is dated in millions of years. You decide to study the relationship among the specimens in each group of fossils by measuring the length of each fossil and graphing it against how old the fossil is. The following graphs show your data for each of these fossil groups. South American Trilobite Species Length of trilobite fossil (Inches) 10 500 375 250 500 375 250 Age of fossil (Millions of years! Age of fossil [Millions of years! had a From these graphs, you can tell a lot about the evolution of each group of trilobites. It appears that the trilobites from lineage stuck in meaning that the species did not change for millions of years. It appears that during the existence of this inches in length. species, individuals averaged around By contrast, the trilobites from appear to have undergone meaning that the lineage diverged to become a group of distinct species that lasted for a period of time. Which of the following statements correctly indicates why a species might undergo adaptive radiation in its evolutionary history? A random mutation introduced a new trait, and the environment introduced new selection pressures on this trait. The species’ environment remained relatively unchanged, so it did not exert new selection pressures on the species. The species’ environment was very strongly selecting for specific traits, and any new traits died out. 9 8 S 4 3 2 1 North American Trilobite Species Length of trilobite fossil (Inches) 10 9 B 7 6 2 1 From these graphs, you can tell a lot about the evolution of each group of trilobites. It appears that the trilobites from lineage stuck in meaning that the species did not change for millions of years. It appears the inches in length. species, individuals averaged around By contrast, the trilobites from appear to have undergone become a group of distinct species that lasted for a period of time. had a tence of this North America South America meaning thartre neage overged to 5 4 3 2 1 0 8 7 6 5 2 1 0 500 375 250 500 375 250 Age of fossil (Millions of years! Age of fossil (Millions of years) had a From these graphs, you can tell a lot about the evolution of each group of trilobites. It appears that the trilobites from lineage stuck in , meaning that the species did not change for millions of years. It appears that during the existence of t inches in length. species, individu adaptive radiation stasis By contrast, the appear to have undergone , meaning that the lineage diverged to become a group at lasted for a period of time. extinction Which of the following statements correctly indicates why a species might undergo adaptive radiation in its evolutionary history? had a From these graphs, you can tell a lot about the evolution of each group of trilobites. It appears that the trilobites from lineage stuck in , meaning that the species did not change for millions of years. It appears that during the existence of this species, individuals averaged around inches in length. 8 By contrast, the trilobites from appear to have undergone , meaning that the lineage diverged to become a group of distinct species th 2 for a period of time. 6 Which of the following statements co dicates why a species might undergo adaptive radiation in its evolutionary history? had a From these graphs, you can tell a lot about the evolution of each group of trilobites. It appears that the trilobites from lineage stuck in , meaning that the species did not change for millions of years. It appears that during the existence of this species, individuals averaged around inches in length. By contrast, the trilobites from appear to have undergone , meaning that the lineage diverged to become a group of distinct sped a period of time. South America Which of the following stateme North America ptes why a species might undergo adaptive radiation in its evolutionary history? A random mutation introduced a new trait, and the environment introduced new selection pressures on this trait. The species’ environment remained relatively unchanged, so it did not exert new selection pressures on the species. The species’ environment was very strongly selecting for specific traits, and any new traits died out. had a From these graphs, you can tell a lot about the evolution of each group of trilobites. It appears that the trilobites from lineage stuck in meaning that the species did not change for millions of years. It appears that during the existence of this inches in length. species, individuals averaged around By contrast, the trilobites from appear to have undergone , meaning that the lineage diverged to become a group of distinct species that lasted for a period of time. stasis extinction in its evolutionary history? Which of the following statements correctly indicates why a species might under A random mutation introduced a new trait, and the environment intro adaptive radiation pressures on this trait. The species’ environment remained relatively unchanged, so it did not exert new selection pressures on the species. The species’ environment was very strongly selecting for specific traits, and any new traits died out.